A conventional paste-type electrode of lead-acid battery is manufactured as follows.
First, an active material containing lead powder as its main component and other required components is kneaded with dilute sulfuric acid or water to prepare a paste-like active material. Then, a current collector made of a lead alloy and having a grid shape is filled with the prepared paste-like active material to obtain a filled electrode. An electrode surface of the filled electrode is pressed to enhance the filling performance of the paste-like active material. After the pressing, the filled electrode is dried. The current collector has relatively thick frame ribs and relatively thin inner ribs unitarily disposed inside the frame ribs to form a grid shape.
Various processes of filling the current collector with the paste-like active material and pressing the electrode surface have been proposed in the related art.
For example, Japanese Patent Application Publication No. 07-245100 (Patent Document 1) discloses a technique in which a current collector placed on a belt conveyor is sequentially transferred and filled with a paste-like active material when the current collector passes below a hopper containing the paste-like active material to fabricate a filled electrode. Then, the filled electrode is caused to pass through a forming roller apparatus, which presses an electrode surface of the filled electrode with a uniform pressure to manufacture an electrode with little fluctuation in thickness. In order to press the electrode surface with a uniform pressure, it is necessary to apply an equal pressure (press load) to both the left and right ends of a forming roller (in the axial direction of the forming roller). Thus, in the technique disclosed in Patent Document 1 discussed above, in order to equalize the pressures respectively applied to both the left and right ends of the forming roller, the forming roller is pressed by one or two cylinders that are actuated by a common pressure.
Japanese Patent Application Publication No. 09-320574 (Patent Document 2) discloses disposing a back-spread improving roller between a belt conveyor and a forming roller to cause a paste-like active material to be sufficiently spread to the lower surface side (opposite to the side of the filled surface to which the paste-like active material is fed) of a current collector. The back-spread improving roller has a hard net on its peripheral surface. The upper surface of the net is covered with a thin fabric or a thin film. When an electrode passes through the back-spread improving roller, the net supports the current collector so that a gap is formed between the current collector and the back-spread improving roller. As a result, the paste-like active material fed to the current collector is pressed into the gap, which deforms the thin film covering the net and, at the same time, fills a space created by the deformation of the thin film with the paste-like active material. Then, the paste-like active material is pressed into a space between the lower surface of inner ribs of the current collector and the back-spread improving roller, which fills a space on the lower surface of the current collector with the paste-like active material. As a result, an electrode in which the inner ribs of the current collector are not exposed to the lower surface side of the current collector is manufactured.